DE2532925A1 - TORSIONAL TABOSCILLATOR - Google Patents

Description

PAl EN IANWmLI E

I EH MLLiH - MÜLLER - STEINMEISTER

D-aOOO Munich 22 D-48OO Bielefeld

IniUUruUe 4 Siekerwali 7

Case W-81

BULOVA WATCH COMPANY, INC

630 Fifth Avenue New York, N.Y. / UNITED STATES

Torsion bar oscillator

The invention relates to a torsion bar oscillator or for short "Torsional oscillator" with which vibrational vibrations of relatively high amplitude can be generated and relates in particular on a torsional oscillator according to the preamble of claim 1, i.e. on one which can be used as an optical scanner Torsional oscillator with a relatively large mechanical bandwidth.

A number of optical devices are already known which act as choppers, scanners, deflectors or in any other way to deflect or modulate light or other in Forir. a beam of existing energy can be used. Such Optical devices are used, for example, in mass spectrometers, thermal converters or bolometers, in color measuring devices or

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Colorimeters, horizon indicators, and various others Instruments installed in which nuclear, X-ray or laser rays or rays in the visible, ultraviolet or Infrared range can be used or analyzed. For some years there has also been a need for ootic scanners with which a beam of light passes over a barrier or barrier or a similar marking device with binary coded marking can deflect to generate signal pulses with which various computer-controllable or a computer-controlling Have functions carried out.

Known optical devices for this purpose usually use motor-driven disks, drums, mirrors or prisms are used which are relatively difficult to adjust and / or have a relatively high energy consumption. Known is also a device with an electromechanically actuated armature that can be rotated or pivoted in precious stone bearings is stored and carries an optical element. However, these optical modulators have so far not been very efficient and show an unstable operating behavior, apart from a great susceptibility to shocks or other vibrations.

These disadvantages of known mechanical oscillators are avoided by a resonance oscillator with a torsional oscillator according to FIG US Pat. No. 3,609,485. This torsional oscillator has an upright torsion bar which is clamped at its foot end, which is electromagnetically excited at a point close to the base point around a point attached to its free end to put the optical element in a reciprocating motion at a speed of motion that is determined by the resonance frequency of the oscillator is determined.

Since the ratio of the angle of twist or oscillation at the free end of the rod in relation to the angle of oscillation at the drive point from Distance between the drive point and the free end of the rod relative to the shorter distance between the drive point and the base point of the rod depends, the deflection of the optical element on

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the free end of the rod is considerably reinforced.

hot dor arrangement according to the said US patent occur, however practical difficulties arise when the drive pulses to Actuation of the rod supplied by an external power source will. The repetition period, i.e. the frequency of the power source supplying the drive signal, is very stable and corresponds to the natural or natural frequency of the torsion bar, this results in a normally large oscillation amplitude at the free end. However, this vibration amplitude becomes strong influenced by changes in ambient temperature which changes the resonance frequency of the rod.

A torsion bar is a mechanical resonator whose natural frequency is determined by its dimensions and Young's vision Modulus of elasticity. The mechanical bandwidth or damping curve of a torsion bar depends on the quality factor, the so-called η value. The bandwidth is narrower or the resonance curve is sharper and sharper, the higher the O value lies. This means that a torsion bar oscillator with high Q value with good efficiency on such drive pulses responds whose sequence or frequency corresponds exactly to the natural frequency of the rod. However, the response characteristic drops sharply when the natural frequency deviates from the frequency of the drive pulses or when the frequency of the drive pulses is opposite the natural frequency of the oscillator is different.

If there is a stable source for the drive pulses and there are deviations in the natural frequency of the mechanical oscillator high Q value from the determined frequency value due to temperature changes affecting the dimensions of the torsion bar, so the amplitude of the rod oscillations drops quite considerably. On the other hand, it is the source of the drive impulses not regulated, so that the repetition sequence of the pulses deviates somewhat from the associated oscillator frequency, so it results also a sharp drop in amplitude, which is determined by the degree of deviation.

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Since, therefore, the highly selective one described in the aforementioned US Pat Torsion bar oscillator has a strong angle sensitivity, if it is fed by an external power source, its frequency due to temperature changes, for example Subject to deviations, such an oscillator can only be operated to a limited extent with good efficiency.

The invention is therefore based on the object of a torsion bar oscillator to create, which has a large mechanical bandwidth at a relatively low Q value, so that the Frequency dependence or frequency selectivity of the oscillator with respect to the drive signal is reduced and the oscillator can nevertheless be operated with good efficiency, even if the frequency of the drive signal depends on the natural frequency of the mechanical oscillator deviates.

The inventive solution to this technical problem is given by de features of claim 1 are denoted for the advantageous developments in subclaims.

The oscillator can be operated with a signal source that is not subject to any particular precision requirements. He draws are characterized by the fact that the amplitude of the mechanical vibrations is maintained at approximately the same level, independently of any deviations in the frequency of the drive signal from the assigned value. On the other hand, there is a highly stable Signal source before, but the natural resonance frequency of the oscillator deviates from the assigned nominal value, for example due to of temperature changes, it is also true in this case that the amplitude of the mechanical vibrations is maintained. The torsion bar oscillator with a low Q value therefore enables reliable operation, even under conditions with which a high Q oscillator would fail.

The rod is set in torsional vibrations by a motor which has an armature which is attached to a so the base of the rod lying point is connected to the rod and interacts with an electromagnet. Of the

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Motor is excited by a drive signal generator whose Frequency is essentially the natural frequency of the oscillator. To dampen the oscillator, the rod is dimensioned so that the one above the anchor point Section has a spring constant which corresponds approximately to that of the section lying below this point. Around to stabilize the mechanical oscillation amplitude is provided in a further development of the inventive concept, a control or Derive control signal from the rod itself as a function of the oscillation amplitude, which is fed to the signal generator and regulates it with regard to the amplitude of the output drive signal.

The invention and advantageous details are described below with reference to the drawing in an exemplary embodiment explained. Show it:

Fig. 1 is a perspective view of a torsional oscillator with the invention Features;

Fig. 2 is a partial sectional view of the oscillator; 3 shows the side view of the oscillator;

Fig. 4 shows the schematic arrangement of the magnetic respectively electrical circuits for the oscillator;

5 shows a schematic representation to illustrate the reinforcing effect of the oscillating movement of the torsion bar;

6 shows a schematic illustration of the damping effect according to the invention on the torsion bar and FIG

7 shows the electrical equivalent circuit diagram to illustrate the damping effect on the rod.

First, the structure of the oscillator is described:

The drawings, and in particular FIGS. 1 to 4, show a torsion bar oscillator which serves as an optical chopper should, in order to modulate an energy beam, convert it into impulses

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your, feel, distract or otherwise steer the impinges on an optical element set in oscillation by the oscillator.

The oscillator has an upwardly projecting torsion bar 1O on, the lower end of which is anchored in a metallic base plate 11, which in turn is on an insulating holding plate 12 rests. On the longitudinal sides of the base plate 11, a pair of upright frame members 13 and 14 is attached, which from a material with soft magnetic properties, for example made of iron. The ends of these elements are provided with inwardly bent lugs 13A, 13B, 14A and 14B, which as Serve pole pieces and define magnetic air gaps. In the figure, only one such air gap 15 is shown, while the other Air gap 16 can be seen in FIG.

Between the frame elements 13 and 14 and in the area of the air gaps standing a pair of permanent magnetic plates 17 and 18 is fitted, the ends of which with the frame members in Are in contact so that the lugs 13A or 13B and 14A or 14B can be polarized in the manner indicated in FIG. I.e. the approaches 13A and 13B become a south or the Approaches 14A and 14B to a north pole so that the lines of magnetic flux extend over the air gaps 15 and 16, respectively.

A soft iron drive anchor is transverse to the rod 10 and symmetrical to it 19 (Figures 2 and 5) are present, the opposite ends of which stand in the air gaps 15 and 16, respectively come. The anchor is attached to a point near the base of the rod. At the rod head 10A, i.e. at the free Enc'e of the rod 10, a second shorter armature 20 is supported in a similar manner, which is aligned with the same vertical plane is like the lower anchor.

A reflection mirror 21 is attached over the tip of the rod 10A, which is rotated back and forth during torsional oscillating movements of the rod 10 about the longitudinal axis of the rod, so that a strikes it Beam of light or other energy beam at one speed

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is periodically deflected by the resonance parameters of the oscillator is determined. The mirror causes a deflection, scanning or chopping of the incident beam. In the present context, the nature of the optical element does not form part of the invention.

One end of the armature 19 is through a first fixed drive coil 22 enclosed, which is glued to the lugs 13A and 14A or firmly connected in some other way. The other The end of the armature 19 is surrounded by a second drive coil 23 which is fastened in an analogous manner to the lugs 13B and 14B. A scanning electromagnet 25 is attached to a rear wall 24 (FIG. 1) near the upper end. This electromagnet works with one end of the upper armature 20 and consists of a coil surrounding a magnetic core. Vibrates the armature 20, a voltage is induced in the electromagnet 25. The drive armature 19, together with the drive coils 22 and 23, forms the motor of the oscillator.

The operating principle of the oscillator is explained below:

The mode of operation of the oscillator can best be illustrated with the aid of FIG. As shown schematically, the Drive coils 22 and 2 3 of the motor are connected to an external supply generator 26 which supplies a drive signal, whose frequency essentially corresponds to the natural frequency of the oscillator.

The subject of the above-mentioned US patent is the feed generator constructed as an electronic amplifier, the input of which is connected to the sensing coil 25, while the output is connected to drive coils 22 and 23 so that there is positive feedback or regenerative switching, which delivers a power, the frequency of which is determined by the mechanical resonance frequency of the torsional oscillator.

/ If the mechanical resonance frequency of the oscillator changes, so

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the power generated by the regenerative circuit also changes, and thus the oscillation amplitude can be maintained .

For many practical applications, however, this is mentioned Feedback arrangement not suitable, for example when the torsion bar oscillator is operated as a scanner, the one Computer system is assigned, in which individual functions are controlled by a clock pulse generator, the pulses in a very specific repetition sequence. The scanner should work to deflect a light beam in such a way that it is binary-coded Markings and pulse trains are created that can be read as computer input signals. To the operation of the scanner to synchronize with the computer, in this case it is necessary to operate the scanner externally by means of a drive signal, which is supplied by a generator under control of the clock pulse generator. This easily creates the Problems mentioned at the beginning, since a comparatively large difference between the operating frequency of the oscillator and the Frequency of the drive signal can occur. In practice, the drive signal can be a sine or square wave or in pulsating form.

Before explaining how these difficulties can be overcome by a avoid appropriately lowering the Q value of the torsional oscillator let, let us first show how the drive signal actuates the oscillator: From Figure 4 it can be seen that the magnetic formed by the lugs 13A and 14A and 13B and 14B, respectively Pole pieces are polarized by the permanent magnets 17 and 18 so that the lugs 13A and 13B are both south poles, while North poles both result for approaches 14A and 14B.

Assume that a drive pulse applied to the coils 22 and 23 increases positively at the moment of observation, the motor armature 19 is polarized in such a way that the one located in the air gap 15 The end south and the other end in the air gap 16 becomes north. The anchor end standing in the air gap 15 thus becomes the north side

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tightened, while the opposite anchor end is pulled in the air gap 16 to the south side and therefore a clockwise acting torque at the anchor point on the torsion bar 10 arises. If, on the other hand, the drive pulse goes negative, then it works the resulting force counterclockwise. In any case, however, the rod is subject to a torsional force.

The natural resonance frequency of the oscillator is determined by the moments of the motor armature 19, the armature 20 and the reflector 21, as well as by the physical parameters and Young's view Modulus of elasticity of the torsion bar 10.

To reduce the influence of temperature on the bar dimensions, the rod can be made of an alloy whose elasticity and body dimensions with temperature changes within a comparatively wide area remain essentially unaffected. Because of the great rigidity of many metals with

Zero temperature coefficient, however, it may be necessary to use alloys such as beryllium copper, which have a larger one Have temperature sensitivity. In this case, the operating frequency of the oscillator inevitably becomes through Affects temperature changes.

The torsional movement of the rod to its resonance frequency causes that the armature 20 vibrates at the same speed, so that a signal voltage is induced in the sensing coil 25. The frequency of this voltage depends on the vibration frequency of the Rod and the amplitude is proportional to the amplitude of the mirror deflection. This signal can also be used in practice win through a pair of sensing coils located on opposite sides of armature 20 and connected in series. This signal voltage can be measured by a measuring device 27 (Figure 4) and use it as a control signal that controls the operation of the external generator via an electronic control device 28 26 determined.

The control device 28 responds to the control signal from the

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Sensing coil 25 and varies the amplitude of the generator output signal so that a constant oscillator signal amplitude is maintained. So in the control device the control signal voltage of the coil 2 5 is compared against a set point or a reference voltage in order to obtain an error signal, which depends on the degree and the direction of the deviation of the oscillator amplitude from a reference level. The error signal is fed to the generator in such a way that there is a zero tendency for the error signal itself and thus the desired one Amplitude level is maintained.

In this context it is of no importance that two drive coils are provided. For a cheaper version of the The oscillator can also have a single armature 19 with a single drive coil at one end and a sensing coil at the other Be provided at the end. This embodiment is in terms of Efficiency not as good as that described above. However, it may be sufficient for some use cases.

Reinforcement of the oscillating movement of the torsion bar:

In order to obtain a large oscillation amplitude for the mirror, it can be seen that there is a large torsional oscillation of the free one Rod end required. If the driving force were to act via the armature in the area of the free end of the rod, it would be relative large air gap required ^ to allow the armature to move. However, if the air gap is large, the magnetic flux density will not be high, so that such an arrangement is ineffective would or might not work at all.

In the structural arrangement according to the invention, the engages Anchor 19 in the vicinity of the base of the torsion bar, it being possible to work with relatively narrow air gaps, so that a high magnetic flux density can be achieved. The displacement of the drive armature is relatively small, but on the other hand is the oscillating movement of the free end of the rod is quite large, since the structure results in mechanical reinforcement.

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As can be seen from the sketch in FIG. 5, the value d corresponds to the short distance between the fastening point of the Drive anchor 19 and the base of the rod, while the value D the long distance between the anchor point of application and the free Ctabende 1OA indicates. With the angle 0 is the oscillation angle of the rod at the anchor point of application and with the angle θ the oscillation angle at the free end of the rod. Because the relationship 0 / Θ = D / d applies, it can be seen that the greater the difference, the greater the angle θ compared to the angle 0 between d and D. If the anchor 19 is arranged near the rod base, it becomes possible to use the torsion rod with relative To drive small oscillating movement and at the same time a large oscillation angle for the attached to the free end of the rod Mirror.

If the torsion bar is excited at a higher natural frequency value, this obviously results in higher operating frequencies. In the case of higher order resonance conditions, for example in the middle of the bar a vibration node and the The scanning armature then does not work in phase with the drive armature. Typical shift values for the mirror are around 10 ° peak to peak at 2,000 Hz and at 3 ° at 10,000 Hz.

The damping:

As mentioned earlier, it is desirable to have the Q value of the torsional oscillator to widen the mechanical bandwidth of the oscillator, which results in a lower frequency selectivity results. This desired reduction in the Q value is achieved by damping the torsion bar 10. This attenuation is illustrated in FIG. It is achieved in that the effective coupling between the tapered section 10X of the rod above the anchor's attachment point and the constant in diameter section 10Y between this anchor point of application and the base of the rod is increased. This increase in coupling is achieved in a manner that advantageously affects the other parameters of the oscillator

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- 12 is matched.

Due to this coupling, a part of the at the free end of the rod to which the mirror or the load element are attached, transmitted via point P to the motor connected to the rod, where via the absorption effect of the magnetic field a damping is effected. The quantitative value of the attenuation is a function of the degree of coupling, the strength of the magnetic field and the geometry of the air gap.

The influence of this coupling on the attenuation can best be seen by considering an electrical equivalent circuit diagram for the Torsion bar and its weight-bearing load, i.e. represent the mirror. Such an equivalent circuit with two closed Figure 7 shows electrical loops. For a fundamental oscillation, the resulting load inertia of the Represent the rod by an equivalent inductance LM and a parallel capacitance CT, which is the spring constant of the tapered rod portion 1OX. The other and higher frequency operating states are through an inductance LA equivalent to the inertia of the drive armature as well as a capacitance CST, which is the spring constant of the straight, i.e. non-conical rod section 1OY corresponds.

Hooke's law teaches, among other things, that the tension in a torsion bar or in any other spring is directly proportional to the force that causes the displacement (provided that the elastic limit of the torsion bar or the spring in general has not been exceeded). The proportionality factor between the displacement and the tension is called the spring constant. The degree of coupling between the sections 10X and 10Y of the torsion bar 10 is determined by the ratio of their spring constants. A maximum coupling results when the spring constants are the same.

If these spring constants, the electrical analogue of which corresponds to a capacitor, are mutually exclusive in terms of their value

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approximated, the degree of coupling between the mirror representing the load and the drive armature is increased. This increase the degree of coupling for any given rod frequency is determined by increasing the stiffness of the tapered section achieved, i.e. in particular by reducing the slope or tapering of this section and by reducing the diameter of the straight, i.e. untapered section 1OY. The relationships can be overlooked from the following relationship:

In this equation are with

w is the resulting frequency, W _{1 is} the angular frequency of the tapered section, w "is the angular frequency of the straight, untapered section

Section,
w is the coupled angular frequency

designated. As the degree of coupling increases, more energy from the mirror load is absorbed by the motor, so that the Q value of the oscillator decreased and the mechanical bandwidth increased. The force developed by the magnetic bias is optimized to achieve a maximum dampening effect. This is achieved primarily through a suitable selection of the operating point of the Magnetic circuit achieved in such a way that it works at the point of maximum energy of the bias magnets.

Although the invention is based on one working as an optical scanner Oscillator has been described in which an optical element has a vibration effect of high amplitude and constant frequency is subject, it can be seen in connection with the explanations given above that the invention is also applicable to numerous other use cases.

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Claims (5)

Claims ζ Λ J Torsion bar oscillator, which can be excited by a periodic signal supplied by an external generator, with an upright torsion bar clamped at the base end, the natural frequency of which can be changed, with an optical element attached to the free bar end, and with a drive motor with an electromagnet that maintains the bar oscillation , which exerts a torque on the rod via an associated armature connected to the rod at a point close to the rod base and excites it to natural frequency oscillations as a function of the periodic signal, characterized in that for generating a coupling between the underneath and the section (10Y or 10X) of the rod (10) above the connection point of the armature (19) and the lower section (10Y) for damping the oscillator and its mechanical bandwidth has almost the same spring constant as the upper section (tOX), whereby un can maintain an oscillator operation with good efficiency depending on any deviation of the frequency of the excitation signal from the rod natural frequency or the rod natural frequency from the frequency of the excitation signal. 2. Torsion bar oscillator according to claim 1, characterized that the upper rod section (10X) tapers conically and the lower rod section (10Y) with the same Surface line spacing is formed over its length. 3. torsion bar oscillator according to claim 1 or 2, characterized in that near the free end of the An armature (20) is attached to the rod (10) and cooperates with a scanning coil (25) to generate a control signal indicating the oscillation amplitude of the optical element. 509886/1082 253232b 4. torsion bar oscillator according to claim 3, dadurc h characterized in that the excitation signal through an external generator (26) can be generated, the amplitude of which is determined by the control signal. 5. Torsion bar oscillator according to one of the preceding claims, characterized in that the rod is made of a beryllium-copper alloy. 509886/108 2